Hands-down, Moose Bog between Island Pond and Ferdinand. I also observed
breeding Black-Backed WPs at Brighton SP last May. Some years ago I watched
in amusement as a "fool's hen" (Spruce Grouse) walked right up to me on the
main trail at Moose Bog, stared at me, and sauntered away! The only place I
have ever seen Boreal Chickadees reliably is Moose Bog - but they seem to
wander widely. My life Black Backed was there, also... although it was so
far away across the bog I really had to spend a long time convincing myself
that the one woodpecker I had been looking for years on end was finally in
my sights.

Check out the Nulhegan Basin (access near Wenlock Crossing) just outside of
Island Pond for these and other birds. May be nearly impossible to traverse
those logging roads this time of year, though.